1. Field of the Invention
This invention relates in general to image regeneration and, in particular, to holographic image regeneration derived from a mathematically defined digital source image by proposing the use of frequency ranges in the electromagnetic spectrum in the non visible ranges. The present invention is further directed to encryption techniques in the coding substrates and decoding devices and their subsequent utility.
More specifically, but without restriction to the particular embodiments hereinafter described in accordance with the best mode of practice, this invention relates to methods for mass manufacturing of two-dimensional microstructures capable of diffracting light.
These specialized amplitude diffraction gratings can be deposited on any type of rigid or semi rigid thermoplastic substrates. The substrate material may include plastic, glass, chemical coatings (e.g. optically-clear adhesive coatings) or any other suitable transparent or semi-transparent rigid or semi-rigid substrate.
The present invention is also directed to apparatus for viewing computer generated holograms (CGH). Such computer generated holograms may be typical CGHs or those encrypted according to the rectangulation methods of the present invention.
2. General Discussion and Related Art
Invisible ink, historically purported to be the most classical method for hiding information is probably considered outdated in today's digital world where numerous covert and overt techniques in the field of coding and decoding exist. Oftentimes complex encryption processes comprising mathematical formulae and electrical engineering based algorithms are used to hide information and reinterpret it after transmission, with appropriate “keys”. The unauthorized copying and theft through the counterfeit manufacture of copyrighted materials, brand names, trademarked property, credit cards, and even individual identities is one of the greatest concerns of both businesses and individuals today. Current measures including distinctive markings, holographic images, photographs, smart chips, and other known techniques that are used to certify the authenticity of products and or identities are proving to be inadequate because they too can be counterfeited.
Industry estimates of worldwide product piracy costs to owners and manufacturers of intellectual property and branded products was approximately $250 billion in the year 2001. Consumers are most often the victims of product piracy unwittingly purchasing counterfeit products believing them to be the genuine articles. The ability to record valuable intellectual property in tags used to authenticate branded goods is fast becoming a necessity. Aspects of the present invention are directed to such tagging and encrypted marking. Such tags or markings can be read and validated by the consumer, retailer, owner, and manufacturer of intellectual property to accurately, and with great precision authenticate, track and protect the value of branded products.
Holograms have been commonly used as security devices. Light reflected from an object is allowed to interact with another coherent beam and the interference pattern caused by the two wave fronts results in a recording medium carrying phase and amplitude information of the object. When the recording medium is subsequently illuminated by a coherent source of light, the virtual image of the object becomes apparent. Some types of holograms are even visible in coherent light. Approaches relying on the use of covert images and special verification equipment exist but there is a continuing need in the art for secure information verification and reliable transmission that can be cost-effectively produced.
The present invention is directed to methods and apparatus for generating, encrypting, and viewing specialized holograms that are mathematically defined. These methods utilize several steps at different levels to ensure a successful encryption process. Thus one aspect of the invention utilizes the generation of Computer Generated Holograms (CGHs) in the encryption process. In one embodiment, the CGH file of an original image is rendered as a binary pattern that can be transmitted onto a substrate by relevant printing techniques. In another embodiment, a binary phase contrast mask performs the binary rendition. An advantage of this procedure is that an image is generated that is invisible to the naked eye unless a point source is viewed through it whereupon a virtual image is generated. The actual pattern that is embossed in the material is impossible to replicate.
Lohman and Paris (Appl. Optics Vol 6. No. 10, 1967) pioneered Computer Generated Holograms or Binary Fraunhofer Holograms. They demonstrated a procedure for creating holograms from objects that could be defined in mathematical terms. They described the selection of a proper format of the hologram and a method using Fourier transformations to develop a pattern of binary information that could reconstruct a mathematical form visually using a point source of light for illumination. Today, several such algorithms exist. In general the algorithm used should be capable of generating data files used to produce Far Field (or Fourier) Holograms (for e.g. Van der Gracht, Am. J. of Phys. (1994) 934-937). A CGH is a diffraction screen whose pattern has been calculated by a computer such that the process of illumination by a point source of light generates the desired image by reconstructing interference patterns.
Laser-assisted reprographic film printers and plotters have been widely used to produce CGHs (Press et al. “The Art of Scientific Computing”, Cambridge, 1989). Similarly, binary amplitude Diffractive Optic Elements (DOEs) are also considered to generate holographic images as indeed they can be defined as holographic elements generated by the interference of two wave fronts that produce components with optical properties. Numerous applications of the generation of computer-assisted holographic DOEs are available (Becker & Dallas Opt. Comm. 15, 50-133, 1975; Gonsalves & Proshaska Proc. SPIES. 938, 472-76, 1988). Currently, photographic duplication using negative films in contact with an original mask is the prevalent method for replicating CGHs originally rendered by the abovementioned reprographic method.
The synthesis of static computer generated holograms can be seen as a two-step process. First an interferometric recording of the diffracted wave field generates the hologram. Then, this unique pattern is transferred to a semi-rigid material and subsequent illumination of this “diffraction grating” is reconstructed by diffraction to generate the CGH.
Many other forms of coherent energy, which are characterized by wave fronts, are also amenable to the methodologies of the present invention thereby enabling any part of the electromagnetic spectrum to be utilized in conjunction with the present invention. Thus in addition to the above use of CGHs, the use of acoustic files as previously confined to the field of acoustic holography, is adapted to the methods of this invention. In these embodiments, the spatial domain of acoustic information is converted into a binary form while the acoustic holographic image is generated.
Generally, holographic planes receiving the reference acoustic energy and the acoustic energy reflected or refracted from the object is scanned by an electronic detector, and used as an indication of the energy available at the receptive points. One way to achieve this is through the system generating a phase related accompanying signal that is able to convert the electrical signals into a binary form whereby the intensity of the created hologram is contained in the amplitude and width of the transparent binary bits employing Fourier transformations.
The addition of random phase noise is required to generate once again a binary output that can also be translated to a rigid substrate. An example of the reconstruction of the final image is performed using digital reconstruction processes that represent inverse transformations of the algorithms thereby generating electronic files representing the original message, when viewed in the reconstructed process.
Jerome L. Pfeiffer awarded in Nov. 19, 1974 U.S. Pat. No. 3,849,758 for “Systems for Making Binary Holograms” describes a system for converting acoustic holograms into binary data. The art of digital data storage in the form of Fourier transform holograms and the use of optical means to decode such transforms can be traced to Alva Knox Gillis et al. in U.S. Patent entitled “Recording and Reading Synthetic Holograms” awarded on Sep. 5, 1978. Subsequently, another disclosed embodiment using electromagnetic waves in the Infra Red (IR) region as one of the information carrying wave fronts is apparent in U.S. Pat. No. 4,880,286 “Making a Holographic Optical Element Using a Computer Generated Hologram” awarded to Charles C. Ih on Nov. 14, 1989. U.S. Pat. No. 4,960,311 “Holographic Exposure System for Computer Generated Holograms” awarded to Gaylord E. Moss and John E. Wreede on Oct. 2, 1990 discloses a system for exposing a recording medium with a computer generated diffraction grating to reduce multiple order scattering noise. U.S. Pat. No. 5,111,445 entitled “Holographic Information Storage System” granted to Demetri Psaltis on May 5, 1992 discusses the use of Fresnel and Fraunhofer holograms to provide a parallel hologram readout method on optical discs. U.S. Pat. No. 5,426,520 entitled “Method of Legitimate Product Identification and Seals and Identification Apparatus” awarded to Kakae et al. on Jun. 20, 1995 provides a method of using a die to emboss a Fourier transform hologram and a device that can identify this seal. U.S. Pat. No. 5,546,198 awarded to Joseph van der Gracht and Ravindra Athale on Aug. 13, 1996 provides an eyeglass/viewing device containing a suitably encoded holographic image. William C Sweatt, U.S. Pat. No. 5,7329,365 entitled “Computer Generated Holographic Microtags” awarded in Mar. 17, 1998, proposes the use of multiple computer generated holograms in submicron size dimensions requiring appropriate decoding readers. U.S. Pat. No. 6,263,104 B1 entitled “Method and Apparatus for Reading and Verifying Holograms” awarded to Stephen McGrew on Jul. 17, 2001, describes the use of scanning a hologram with a laser beam and analyzing the diffraction pattern, thereby making this a generalized extension of several (earlier) reading devices that required specially adapted holograms.